The present invention relates in general to a storage apparatus system for carrying out the copy (the remote copy) of data to another storage apparatus system which is located in an out-of-the-way place. More particularly, the invention relates to an information processing system for carrying out the remote copy which is of the type in which the order of writing data from a host computer to a storage apparatus system does not match the order of transmitting data from a storage apparatus system having the data written thereto to another storage apparatus system.
In an information processing system having a host computer and a plurality of storage apparatus systems, as the technology of carrying out the copy of data between the storage apparatus systems, there is known the remote copy.
By the remote copy is meant the technology in which a plurality of storage apparatus systems which are located physically apart from one another carry out the copy of the data, i.e., the double writing of the data between the storage apparatus systems without interposition of the host computer.
The storage apparatus system is a system including a plurality of storage apparatuses and a controller for controlling these storage apparatuses.
In the information processing system which carries out the remote copy, the storage apparatus systems which are respectively arranged in the places physically remote from one another are electrically connected to one another through dedicated lines or public lines. Of logical storage areas (hereinafter, referred to as “logical volumes”, when applicable) which a certain storage apparatus system has, the logical volume having the same capacity as that of the logical volume subjected to the remote copy (hereinafter, referred to as “the source volume” for short, when applicable) is ensured in the storage apparatus system to which the source volume is copied. This ensured logical volume (hereinafter, referred to as “the destination volume”, when applicable) is formed in such a way as to show one-to-one correspondence relation with the source volume.
The data of the source volume is copied to the destination volume through the associated one of the dedicated lines or public lines.
When the data contained in the source volume is updated, the updated data is transferred to the storage apparatus system having the destination volume through the associated one of the dedicated lines or the like and the updated data is also written to the destination volume corresponding to the source volume.
If the technique of the remote copy is employed, then in the information processing system having a plurality of storage apparatus systems, the logical volume of the same contents can be held in a plurality of storage apparatus systems.
The technique relating to the remote copy is disclosed in U.S. Pat. No. 5,742,792. In U.S. Pat. No. 5,742,792, the technique called the adaptive copy is further disclosed.
By the adaptive copy is meant one of the remote copy techniques. The adaptive copy is the remote copy method wherein before the data written from the host computer to the local storage device is copied to the remote storage device, the information exhibiting the completion of write is returned back to the host computer.
In the adaptive copy, the transmission order of data is not serialized, and hence the order of writing the data to the source volume by the host computer may be different from the order of transferring these data to the destination volume in some cases (hereinafter, such remote copy is referred to as the remote copy of “no guarantee to order”, when applicable).
When the host computer writes repeatedly data to the same location in the destination volume on the basis of that property, only the data which has been written thereto lastly can be transmitted to the storage apparatus system having the destination volume. Therefore, the load on the network such as the dedicated line between the storage apparatus systems can be reduced.
On the other hand, when the host computer in which the file system used in the so-called open system is incorporated writes the data to the storage apparatus system, in general, the buffer and the like provided in the host computer, whereby an instruction to transfer the data from an application program to the file system is made asynchronously with the operation of writing the data to the storage apparatus system.
But, in the case that the data in the file is destroyed due to various problems, in order to keep the coherency of the file system structure, with respect to at least the directory and the meta-data such as i-node which are used to manage the file system, the operation of issuing an instruction to transfer the data, i.e., the directory and the meta-data from the host computer to the storage apparatus system is carried out synchronously with issuing of the write command from the application program running on the host computer to the file system. The above-mentioned technique is disclosed in an article of “The Design and Implementation of a Log-Structured File System”, Mendel Resenblum and John K. Ousterhout, ACM Transactions on Computer Systems, Vol. 10, No. 1, February 1992, page 29.
By executing such a processing, even if the data in the file which is buffered in the host computer is lost due to the asynchronous writing by an abrupt power source shutdown or the like, the meta-data is not lost at all. So, the coherency of the file system structure is kept and the damage can be kept to a minimum even though the data itself is lost.